1. Field of the Invention
The present invention relates to a toner for electrophotography, and more particularly to a method of preparing a toner by dripping a toner constituent liquid through a nozzle.
2. Discussion of the Background
Recently, the electrophotographic copiers or printers are required to produce images having higher quality. In order to satisfy this requirement, toners are actively studied to have smaller particle diameters.
Conventionally, pulverization methods of melting and kneading a binder resin and a colorant to prepare a kneaded mixture, pulverizing the kneaded mixture and classifying the pulverized mixture have been used. However, the pulverization methods prepare toners having wide particle diameter distributions, and have limitations of technically reducing diameter and of productivity such as yield.
Recently, polymerized toners prepared by suspension polymerization methods, emulsion polymerization condensation methods, etc. are being used. Besides, Japanese published unexamined application No. 7-152202 discloses a polymer solution suspension method of using a volume contraction. This method includes dispersing or dissolving toner constituents in a volatile solvent such as an organic solvent having a low boiling point to prepare a dispersion or a solution, emulsifying the dispersion or solution in an aqueous medium to form a droplet, and removing the volatile solvent. The diversity of resins this method can use is wider than those of the suspension polymerization methods and emulsion polymerization condensation methods, and has an advantage of being capable of using a polyester resin effectively used for full-color images requiring transparency and smoothness.
However, in the polymerization methods, since a dispersant is basically used in an aqueous medium, the dispersant impairing the chargeability of a toner remains on the surface thereof, resulting in deterioration of environmental resistance. In addition, a large amount of water is needed to remove the dispersant, resulting in unsatisfactory methods of preparing a toner.
Japanese published unexamined application No. 2003-262976 discloses a method and an apparatus forming a microscopic droplet with a piezoelectric pulse, and drying and solidifying the microscopic droplet to form a toner. Further, Japanese published unexamined application No. 2003-280236 discloses a method of forming a microscopic droplet with a heat expansion in a nozzle, and drying and solidifying the microscopic droplet to form a toner. Further, Japanese published unexamined application No. 2003-262977 discloses a method of forming a microscopic droplet with an acoustic lens, and drying and solidifying the microscopic droplet to form a toner.
In these methods of spraying microscopic droplets, organic solvents having small latent heats are energetically preferably used in a solution or a dispersion to be sprayed. However, the organic solvents remaining in the resultant powder are very difficult to remove.
Because of these reasons, a need exists for a method of spraying a toner constituent liquid formed of toner constituents dissolved in an organic solvent to form a microscopic droplet and drying the microscopic droplet to form a toner, which is capable of drying the microscopic droplet at low cost and short times.